Patients with ductal carcinoma in situ (DCIS) have significant risks of developing recurrence or invasive breast cancer even after they receive breast surgery. Thus, women stand to benefit from chemoprevention strategies that reduce the incidence of DCIS recurrence. However, the molecular mechanisms that underlie DCIS development remain unclear and so it is important to identify pathways that could be targeted for prevention. Our preliminary studies showed that loss of microRNA-140 (miR-140) expression is associated with the development of DCIS and that sulforaphane (a key bioactive ingredient of cruciferous vegetables) can restore miR-140 expression in primary DCIS cells. We further observed that reduced miR-140 expression is associated with increased expression of the SIRT1 histone deacetylase that is associated with enhanced cancer stem cell survival. Finally, miR-140 knockout mice spontaneously developed DCIS at 11 months of age. Our preliminary data suggest that miR-140 and SIRT1 have roles in DCIS development. Based on these results, we hypothesize that miR-140 loss leads to increased SIRT1 expression which drives DCIS development and increased accumulation of breast cancer stem cells. We further propose that sulforaphane treatment can restore miR-140 level which then targets and suppresses SIRT1 level to prevent DCIS development. Specific Aim 1 will define the mechanism of miR-140 inactivation in DCIS transformation. Specific Aim 2 is designed to determine the impact of miR-140 on cancer stem cell survival in DCIS transformation. Specific Aim 3 is designed to characterize the role of miR-140 in sulforaphane chemoprevention of DCIS in vivo. We believe that these studies are innovative and high impact because findings from our studies will identify a new mechanism of DCIS development and a new route of sulforaphane-dependent breast cancer prevention. We have developed all of the cell-based and animal models necessary to complete these studies. PUBLIC HEALTH RELEVANCE: Our studies strongly suggest that sulforaphane may be an important chemopreventive agent to suppress DCIS by correcting the epigenetic regulation to restore miR-140 expression.